FIG. 1 illustrates a simplified block diagram of the transmitting subsystem 100a of a prior-art KVM Extender having multiple optical fibers 62. Optical fiber 62 may be single-mode or multi-mode types. The number of optical fibers 62 used may vary between products and it is typically between 2 and 6. In this prior-art system computer 1 is the being operated remotely by a user located at the receiving subsystem 100b illustrated in FIG. 2 below.
The term KVM Extender implies that the fiber media is used to extend Keyboard Video Mouse. Still many prior-art KVM Extender products support other interfaces such as bi-directional audio and serial communications.
Prior-art KVM Extenders are divided in two general classes based on the media used to link both ends:                Copper KVM Extenders typically uses Ethernet cables as a link media. This type of products is limited in distance to few hundred meters due to signal quality degradation.        Fiber optic KVM Extenders that uses one or more optical fibers. This type of products can reach distances as long as 20 km.        
In this FIG. 1 and in all other figures—only fiber optic KVM Extender is shown.
Computer 1 (for example, but not limited to a PC computer) is coupled to the KVM Extender device 40 through a set of cables. Display output port 2 illustrated here as a digital output, may be DVI-D (Digital Video Interface), HDMI (High-Definition Multimedia Interface), DisplayPort or any other suitable standard. Four TMDS (Transition Minimized Differential Signaling) lanes of the display output 2a are coupled through differential pairs 22a to 22d inside the video or extender cable. The DDC (Display Data Channel) or EDID (Extended display identification data) interface section of this interface 2b provides Plug and Play data exchange between the coupled display and the computer 1. In this example, the DDC/EDID lines 28 of computer 1 are coupled to the KVM extender 40 through KVM Extender cable or video cable 29 together with the differential pairs 22a to 22d. 
Legacy VGA (Video Graphics Array) standard may be coupled if prior-art KVM Extender transmitter 40 supports analog to digital conversion.
Audio out stereo jack 3 is coupled with a shielded cable 24 and 25 to extend the analog audio output over the fiber link 62. Audio extension is optional and is model dependant.
Audio output may be supported through the four display output lanes connected with differential pairs 22a to 22d if protocol used is HDMI or DisplayPort.
Audio input or microphone input jack 4 is coupled to the KVM Extender transmitter 40 through another shielded cables 26 and 27 to enable remote extension of the user microphone over the fiber link 62.
Computer 1 USB (Universal Serial Bus) port 5a is coupled to the KVM Extender transmitter 40 through USB cable 30 to enable remote extension of the user keyboard and mouse over the fiber link 62. A single USB port is typically used to deliver all USB port traffic through a USB hub located at the KVM Extender receiver subsystem.
Additional USB port 5b may be coupled to the KVM Extender transmitter 40 through another USB cable 32 to enable remote extension of other type of user peripherals such as USB mass-storage device or smart-card reader.
Some prior-art KVM Extenders 40 also support serial communication (RS-232) to enable certain control functions such as KVM control or conference room management functions. If supported, computer serial port 9 is coupled to the KVM Extender transmitter 40 through serial cable 34.
External power supply 20 coupled to the KVM Extender transmitter unit 40 through cable 87 provides low voltage DC power to supply all internal circuitry. Some prior-art KVM Extender models having larger enclosure are fitted with internal AC/DC (Alternating Current/Direct Current) power supply module.
All cables coupled to computer 1 are connected to the KVM Extender transmitter Printed Circuit Board 42 that handles all signal processing required. Typical functions including:
1. Establishing a link with the receiver subsystem before exchanging data.
2. Emulating DDC/EDID to the coupled computer 1 based on the display connected remotely at the other side.
3. Emulating keyboard to deliver remote user keyboard inputs to computer 1.
4. Emulating mouse to deliver remote user mouse inputs to computer 1.
5. Streaming the audio channels over fiber media—converting analog audio into digital steam (Analog to Digital Conversion) and vice-versa (Digital to Analog Conversion).
6. Streaming of digital video components over the fiber media.
7. Streaming of USB traffic to support various high speed peripherals.
8. Provide user interaction (user inputs and monitoring) of the device status and modes of operation.
In this prior-art KVM Extender, there are 2 optical fibers 62:                One optical fiber is coupled to the fiber optic transmitter module 46 that is used to transmit data from KVM Extender transmitter subsystem 40 to the KVM Extender receiver 80 of FIG. 2 below.        Another optical fiber is coupled to the fiber optic receiver module 44 that is used to receive data from KVM Extender receiver subsystem 80 of FIG. 2 below.        
The KVM Extender transmitter Printed Circuit Board 42 converts all transmitted data such as video lanes, audio output, USB output etc. into a single high-speed data stream coupled to the fiber transmitter module 46 through a differential pair 50.
In the reverse direction all data received by the fiber optical receiver module 44 is coupled to the KVM Extender transmitter Printed Circuit Board 42 through differential pair 55 and separated back into various inputs such as USB keyboard, mouse, EDID etc.
Power to the fiber optic transmitter module 46 is delivered from the KVM Extender transmitter Printed Circuit Board 42 through line 48 and it is passed through the module connector 47.
Power to the fiber optic receiver module 44 is delivered from the KVM Extender transmitter Printed Circuit Board 42 through line 54.
Optical fibers 62 may be permanently attached to the optical fiber transmitter and receiver modules 46 and 44 or coupled through a removable interconnect 61 such as LC (Lucent Connector) or SC (Subscriber Connector) that fits into a matting housing 60. Fixed optical fibers are less flexible and harder to deploy but typically cost less than systems having fiber optical interconnect.
FIG. 2 illustrates a simplified block diagram of the receiving subsystem 100b of a prior-art KVM Extender having two optical fibers 62. In this prior-art system user console peripherals are coupled to the KVM Extender receiver device 80 that is remotely coupled to the computer 1 shown in FIG. 1 above.
All received data from optical fiber 62 coupled to optical fiber receiver module 44. Optical fiber receiver module 44 coverts the received optical signals into a differential electrical signal that is coupled through differential lines 82 and via the module connector 45 into the KVM Extender receiver Printed Circuit Board 86. The KVM Extender receiver Printed Circuit Board 86 processes that data received and coverts it back to the required peripheral protocols such as digital video and audio to drive user peripheral devices.
All data from local user peripheral devices is processed by the KVM Extender receiver Printed Circuit Board 86 and then passed through differential pair 84 into the optical transmitter module 46 via the module connector 47. The optical fiber transmitter module 46 converts the incoming data stream into light signals passed through optical fiber 62.
Power supply 20 coverts the mains AC voltage into low DC voltage that is passed through DC cable 87.
User display 90 is coupled to the KVM Extender receiver Printed Circuit Board 86 through video cable 89 made of four differential pairs 88a to 88d and EDID lines 99. A microcontroller inside the KVM Extender receiver Printed Circuit Board 86 reads the coupled display 90 EDID information and stream it over the optical fiber 62 to the transmitter subsystem computer 1.
User headsets or amplified speakers 96 are coupled to the KVM Extender receiver Printed Circuit Board 86 through audio out lines 91 and 92 and microphone in lines 93 and 94. The KVM Extender receiver Printed Circuit Board 86 coverts incoming data stream into analog audio through stereo Digital to Analog Converters (DACs) and incoming microphone analog signal into a digital stream through Analog to Digital Converter (ADC).
User keyboard 97 is coupled to the KVM Extender receiver Printed Circuit Board 86 through USB cable 98. In KVM Extender receiver Printed Circuit Board 86 the keyboard USB or PS/2 keystrokes information is sent over the fiber media 62 into the transmitter subsystem KVM Extender device 40 and into the coupled computer 1. Similarly, the user mouse 997 is coupled to the KVM Extender receiver Printed Circuit Board 86 through cable 102.
Optional smart-card reader 105 or other USB device may be coupled to the KVM Extender receiver Printed Circuit Board 86 through USB cable 104. All data received from that device 105 is transmitted over the optical fiber 62 into the transmitter subsystem KVM Extender device 40 and into the coupled computer 1 of FIG. 1 above.
Optional serial device 998 such as remote controller is coupled through RS-232 cable 106 into the KVM Extender receiver Printed Circuit Board 86. Serial output data is transmitted over the optical fiber 62 into the transmitter subsystem KVM Extender device 40 and into the coupled computer 1 serial port 9 of FIG. 1 above.
This prior-art KVM Extender suffers from several disadvantages:                It relies on multiple optical fibers to link between the ends. Multiple optical fibers are expensive and harder to deploy. It is also less reliable as one fiber link failure may prevent system usage.        The KVM Extender receiver and transmitter Printed Circuit Boards 42 and 86 are complex and expensive to make. It also consumes a lot of power and therefore cannot be powered by computer 1.        It does not support link security functions that may be needed in order to link between the user and a Secure KVM switch or secure KVM matrix devices.        